The present invention relates to dental devices, and in particular to a hand held motor driven prophylaxis device for use in the home.
Many motorized detal instruments have been developed for home use. Such devices promote effective and efficient dental hygiene and reduce the frequency with which a dentist must be consulted. Attempts have also been made to develop a polishing instrument so that this function can be performed in the home as well. However, many difficulties have been encountered in developing such a device.
A polishing instrument for home use must be both simple and inexpensive to manufacture so that it can be produced at reasonable cost. It is thus advantageous to construct such a device from plastic material, molding the device in sections and joining the sections together. This type of structure is relatively flexible, and a bearing is required near the electric motor of the device to prevent excessive movement of the drive shaft. The drive shaft passes through a plastic shank running from the handle of the device to the polishing head, and this shank will ordinarily bend significantly when the instrument is being used because of the pressure on the polishing head.
If a ball bearing or other known type of bearing is used to fix the position of the drive shaft, the bearing will act as a fulcrum for the side loads imposed on the polishing head. The distance from the bearing to the polishing head is much greater than the distance from the bearing to the motor, and as a result, the side loads on the polishing head will be accentuated by the bearing. Relatively large side forces will thus be imposed on the electric motor, these side forces being greater than the forces imposed on the polishing head itself. Since the polishing head must be operated at relatively low speed to be effective, the electric motor has a relatively low capacity and these accentuated forces will cause the motor to bind.